String

Arezoo Sh

15y3.4kC#

I want to reverse the string, is there any method in .Net 2010 do that? with C#lan
forexample:
    string s2= "abcdefg";
    but I want that "gfedcba" is written.
    Console.WriteLine(s2); // gfedcba

8 Replies

Know the answer? Post it — somebody with the same question will find it here.

Vulpes15y ago
Thanks Hirendra :)

Incidentally, I forgot to answer Suthish's question about why gamers might be interested in the 'unsafe' approach.

The answer quite simply is that such folk are usually looking for the quickest way to do something in their chosen language and don't mind using every trick in the book to achieve it.
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Hirendra Sisodiya15y ago
good job Vulpes......
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Vulpes15y ago
It is C# code though, when you use 'unsafe', it looks and feels like you're programming in C .

I use the System.Diagnostics.Stopwatch class for timing code. Here's what I used to do the timings in this particular case over 1 million iterations for each approach:

using System;
using System.Diagnostics;
using System.Linq;

class Test
{
static void Main()
{
string s = "abcdefghi";

Stopwatch sw = Stopwatch.StartNew();
for(int i = 0; i < 1000000; i++)
ReverseString(s);
sw.Stop();
Console.WriteLine("Unsafe approach took {0} ms ",sw.ElapsedMilliseconds);

sw = Stopwatch.StartNew();
for(int i = 0; i < 1000000; i++)
{
char[] chars = s.ToCharArray();
Array.Reverse(chars);
s = new string(chars);
}
sw.Stop();
Console.WriteLine("Array.Reverse approach took {0} ms", sw.ElapsedMilliseconds);

sw = Stopwatch.StartNew();
for(int i = 0; i < 1000000; i++)
{
s = new string(s.Reverse().ToArray());
}
sw.Stop();
Console.WriteLine("Enumerable.Reverse took {0} ms", sw.ElapsedMilliseconds);

Console.ReadKey();
}

unsafe static void ReverseString(string s)
{
if (s == null || s.Length < 2) return;
int len = s.Length;

fixed (char* ps = s)
{
char* pc = ps;
int i = 0;
int j = len - 1;
char c;
while (i < len/2)
{
c = pc[i];
pc[i++] = pc[j];
pc[j--] = c;
}
}
}
}

You'll need to repeat it a few times and take the avarage. Even then, it's not very scientific as we should be testing strings of different lengths, over different numbers of iterations and on different CLR/OS combinations but it's enough to give you a quick indication of relative speed.
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Suthish Nair15y ago

Vulpes,

Interesting and Thanks for sharing.

Have Couple of doubts, for knowledge :)

How can i test below statement

"the following is a very fast method for reversing a string - about 12 times faster than ....."

Why you said this way is good for gamers because which manipulate memory directly using pointers?

Is this pure C# or C, am sorry if this a stupid question..
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Vulpes15y ago
For the benefit of those who do games programming, the following is a very fast method for reversing a string - about 12 times faster than Array.Reverse() and 80 times faster than Enumerable.Reverse():

using System;

class Test
{
static void Main()
{
string s = "abcdefg";
ReverseString(s);
Console.WriteLine(s);
Console.ReadKey();
}

unsafe static void ReverseString(string s)
{
if (s == null || s.Length < 2) return;
int len = s.Length;

fixed (char* ps = s)
{
char* pc = ps;
int i = 0;
int j = len - 1;
char c;
while (i < len/2)
{
c = pc[i];
pc[i++] = pc[j];
pc[j--] = c;
}
}
}
}

However, methods like this which manipulate memory directly using pointers are best avoided in normal application code - stick to the 'safe' methods.
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Suthish Nair15y ago
string s2 = "abcdefg";
Console.WriteLine(s2);
Console.WriteLine(s2.ToCharArray().Reverse().ToArray());
Console.ReadKey();
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Amit Choudhary15y ago
Try below code:
Using System.Linq;
String str = "aabcadfdsf";

Console.WriteLine(str.Reverse().ToArray<Char>());
Hope this was helpful.

Thanks.
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Jiteendra Sampathirao15y ago
hi,

string str= "jiteendra";
char[] reverse = str.ToCharArray();
Array.Reverse(reverse );
string StringReverseOrder = new string(reverse);

i hope it help you.........
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